What Is a Transformer for Solar Power System? (10kV & 35kV Explained)

A transformer for a solar power system is a critical electrical device that enables photovoltaic (PV) power plants to deliver electricity into the utility grid. Since solar panels and inverters generate low-voltage electricity, typically at 0.4kV or 0.8kV, this voltage must be stepped up to medium or high voltage levels such as 10kV, 35kV, 110kV, or higher before transmission.

Without transformers, solar energy cannot be efficiently transmitted over long distances or safely integrated into the grid.

In modern utility-scale solar projects, especially ground-mounted solar farms, the most commonly used configurations involve:

10kV distribution transformers for medium-scale systems

35kV step-up transformers for large-scale solar power plants.

The 10kV or 35kV solar transformers manufactured by Jiangsu Unita Electric can meet your project requirements, with customizable capacities for both high and low voltage sides.

1. Why Solar Power Systems Need Transformers

Solar power systems generate electricity in direct current (DC) form, which is then converted into alternating current (AC) by inverters. However, the output voltage from inverters is relatively low and not suitable for grid transmission.

A transformer is required to:

1.1 Step Up Voltage for Grid Connection

Electricity must be transmitted at higher voltages to reduce energy loss. When voltage increases, current decreases, which significantly reduces line losses.

This is especially important in large solar farms where power must travel long distances to substations.

1.2 Improve Transmission Efficiency

Higher voltage levels reduce:

• Resistive losses (I²R losses)
• Cable heating
• Energy waste over transmission lines

1.3 Enable Grid Compatibility

Transformers ensure solar plants match these grid requirements.

1.4 Provide Electrical Isolation

Transformers also isolate the solar plant from the grid, improving safety and protecting equipment from faults and surges.

2. What Is a Step-Up Transformer in Solar Plants?

A step-up transformer is an electrical device that increases voltage from a lower level to a higher level.

In solar power systems, it is typically installed between:
inverter output → transformer → switchgear → grid connection

Key Functions:

• Voltage elevation (e.g., 0.8kV → 10kV or 35kV)
• System stabilization under fluctuating solar generation
• Grid compliance and synchronization
• Harmonic reduction support in some designs

Common Types Used in Solar Plants:

• Oil-immersed transformers (most widely used for outdoor PV farms)
• Pad-mounted transformers (compact installations)
• Box-type substations (integrated transformer + switchgear + protection system)

Jiangsu Unita Electric can provide all above products for your solar power system, and all of them can be customized according your need.

Oil-immersed transformers dominate utility-scale projects due to their:

• High efficiency
• Strong heat dissipation：Oil nature Air Nature
• Long service life: The service life of Jiangsu Unita oil-immersed transformer over 25 years
• Excellent overload capability

3. 10kV vs 35kV in Solar Power Plants

One of the most important design decisions in a solar project is choosing the correct voltage level for collection and step-up systems.

3.1 10kV Solar Transformer Systems

10kV systems are commonly used in:

• Small to medium-sized solar power plants
• Distributed photovoltaic projects
• Industrial or regional energy systems

Typical characteristics:

• Capacity range: 500kVA to 2500kVA
• Lower installation cost
• Simpler grid connection
• Suitable for short-distance power transmission

Advantages:

• Lower upfront investment
• Easier maintenance
• Flexible deployment in modular solar farms

Limitations:

• Higher transmission losses compared to 35kV systems
• Limited capacity for large-scale solar farms

3.2 35kV Solar Transformer Systems

35kV systems are widely used in utility-scale solar power plants.

They are typically found in:

• Large ground-mounted solar farms
• National grid-connected renewable energy stations
• Centralized photovoltaic power plants

Typical characteristics:

• Higher transmission efficiency
• Used for collector systems (multiple inverters aggregated)
• Step-up to 110kV or 220kV grid substations

Advantages:

• Reduced power losses over long distances
• Better suited for large-scale energy generation
• Fewer transformer units required per MW

Limitations:

• Higher equipment cost
• More complex protection and design requirements

3.3 Key Differences Between 10kV and 35kV

Feature	10kV System	35kV System
Application scale	Small/medium PV plants	Utility-scale solar farms
Transmission efficiency	Medium	High
Investment cost	Lower	Higher
Grid integration level	Local distribution	High-voltage transmission
System complexity	Simple	Advanced

4. Centralized vs Distributed Solar PV Architecture

Solar power systems are generally divided into two main architectural types.

4.1 Distributed Solar Power Systems

Distributed systems are typically installed on:

• Rooftops
• Industrial facilities
• Small ground-mounted plants

Characteristics:

• Short power transmission distance
• Lower voltage levels (often 10kV or below)
• Local consumption or small grid feed-in

Transformer usage:

• Smaller distribution transformers
• Often integrated into compact substations

4.2 Centralized Solar Power Systems

Centralized systems refer to large-scale solar farms located in open areas such as deserts or plains.

Characteristics:

• High power output (tens to hundreds of MW)
• Long-distance transmission to substations
• Use of 35kV collector systems

Transformer usage:

• Large capacity step-up transformers
• Multiple inverters aggregated into one transformer unit
• Connection to high-voltage grid (110kV/220kV)

5. Key Functions of Solar Power Transformers

Solar transformers are not just voltage conversion devices. They perform multiple critical roles in photovoltaic power systems.

5.1 Voltage Conversion

Primary function: stepping up inverter output to grid-compatible voltage levels.

5.2 System Protection

They protect equipment from:

• Overload conditions
• Short circuits
• Voltage spikes

5.3 Electrical Isolation

They ensure safe separation between:

• Solar generation system
• Utility grid

5.4 Thermal Management

Oil-immersed designs efficiently dissipate heat, ensuring stable operation in high-temperature environments such as deserts.

5.5 Grid Stability Support

Transformers help maintain voltage stability during:

• Solar irradiance fluctuations
• Load variations
• Grid disturbances

6. How to Select the Right Transformer for a Solar Power Project

Choosing the correct transformer is critical for system performance and long-term reliability.

Key selection factors include:

6.1 System Capacity (kVA / MVA)

Transformer size must match inverter output and total plant capacity.

6.2 Voltage Level

• 10kV for smaller distributed systems
• 35kV for utility-scale solar farms

6.3 Environmental Conditions

Important for outdoor PV plants:

• High temperature regions
• Desert environments
• Coastal corrosion areas
• High-altitude installations

7. FAQ – Solar Power Transformers

What is the voltage of a solar power transformer?

Most solar transformers operate at medium voltage levels such as 10kV or 35kV, depending on plant size.

Why do solar farms use 35kV transformers?

Because higher voltage reduces transmission losses and improves efficiency in large-scale solar farms.

Can 10kV transformers be used in solar plants?

Yes, but mainly in small to medium distributed solar projects.

What type of transformer is used in solar PV systems?

Oil-immersed step-up transformers are most commonly used in utility-scale solar farms.

What is the lifespan of a solar transformer?

Usually the lifespan is more than 20 years. You can choose Jiangsu Unita products, the lifespan of them is over 25 years.

Does the voltage of a transformer could be customized?

Yes, sure. The voltage can be customized to suit your project.

Conclusion

Transformers are essential components in every solar power system, enabling efficient voltage conversion, grid integration, and system stability.

The choice between 10kV and 35kV systems depends on project scale:

• 10kV for distributed and medium-sized solar projects
• 35kV for large utility-scale solar farms

Understanding transformer selection is crucial for EPC contractors, project developers, and power utilities aiming to optimize performance and reduce long-term costs.